Evidence of human habitation in Corinthia dates back to the Neolithic Era, with stone tools and Bronze Age pottery indicating continuous occupation. The population declined during the Greek Dark Ages, leading to a loss of material wealth in Isthmia.

During the Archaic period, Isthmia saw a revival in writing, culture, and population growth, marked by the construction of significant monuments. Isthmia became a hub for Greek conferences during the Persian invasions. A temple dedicated to Poseidon was damaged by fire in 480 BCE and later rebuilt with Classical elements. Following a fire during the Corinthian War in 390 BCE, Isthmia experienced economic decline. The site played a crucial role in political events during the reign of Philip II and Alexander the Great.

A permanent settlement arose near the temple in the late 4th century BCE but was destroyed by the Romans in 198 BCE during the Second Macedonian War. The declaration of Greek freedom by Titus Quinctius Flamininus established Isthmia as a symbol of Greek unity. After the destruction of Corinth in 146 BCE, control of the Isthmian Games passed to Sicyon, but they returned to Corinth following its refoundation as a Roman colony in 44 BCE. Emperor Nero visited in 67 CE, and further construction occurred in the 2nd century CE.

In the 4th century CE, Emperor Constantine prohibited pagan practices at Isthmia, leading to the decline of the Temple of Poseidon. The site’s materials were repurposed for defensive walls in the 5th century. The Ottomans captured Isthmia in the early 15th century, controlling it amidst conflicts until the Greek War of Independence.

Oscar Broneer discovered the site in 1952, conducting excavations that revealed the temple, theater, and stadiums associated with the Isthmian Games until 1967. His findings were published starting in 1971. Elizabeth Gebhard continued the work in 1976, leading further excavations in 1989 to address disputes regarding Broneer’s conclusions. Subsequent excavations focused on various periods, particularly the Archaic temple. Later excavations from 1967 onward examined Roman and Byzantine structures.

circa 650-470 BCE

Archaic Temple of Isthmia
The Temple of Isthmia, an ancient Greek temple on the Isthmus of Corinth, was dedicated to Poseidon and initially built during the Archaic Period. Located about 16 kilometers (9.9 miles) east of ancient Corinth at the site of ancient Isthmia, the temple is thought to have been constructed in the seventh century BCE. Around this time, a transformative period in Greek architectural and artistic history was emerging. Corinth played a central role in this transition, contributing advancements in pottery design, settlement planning, military organization, and most notably, the rise of monumental buildings and the Doric order of architecture. The construction date of the Archaic temple is significant as it marks the onset of monumental architecture in Greece and the shift from Iron Age architectural styles to the more defined Doric style, shaping the form of the Greek temple as a whole. The first temple, constructed in this early period, was later destroyed by fire in 470 BCE.

circa 582 BCE

Early Stadium
The Isthmian Games, established in 582 BCE, led to the construction of a stadium specifically for athletic events, which has since been termed the Early Stadium. This stadium, located immediately southeast of the Temple of Poseidon, was equipped with water channels, a well-preserved starting line, and remnants of an artificial embankment along the track’s northern side, enabling spectators to watch the contests. The water channel circled the outer edge of the running track and flowed through two basins on opposite sides of the starting line, supplied with freshwater through openings in the surrounding walls. A sophisticated starting mechanism was also built to ensure fair starts for footraces, consisting of a triangular pavement with sockets for a row of upright posts flanking the sixteen lanes. Shallow grooves extended from these sockets to a single round cutting at the pavement's apex, marking the starter's position. The upright posts supported a horizontal wooden bar attached to a string, which the starter could release, causing it to drop vertically. Despite its ingenuity, this mechanism may not have worked as planned and was soon replaced by simpler starting methods using a single barrier.

circa 510-323 BCE

Classical Greek Baths
A bathing establishment of Classical Greek date lay under the floor of the Roman period bath compelx, showing that this spot was used for bathing for nearly a thousand years. The full extent of the Greek period bath has not yet been exposed or excavated and, of course, much of it is still concealed under the walls and floors of the Roman era building. Nonetheless, a number of features associated with the Greek bath can still be discerned.

The most visible feature of the classical Greek bath is the floor of the large plunge pool. This can be seen underlying the work area in the southern part of the apsidal chamber with the hypocaust system. The floor is featureless and is made of waterproof cement. The wall associated with this floor can be seen running underneath the main south wall of the Roman period bath complex, to the south of the apsical hypocaust chambers; it is at a slightly different orientation than rest of the walls of the Roman period building. Three of the corners of this pool have been found, allowing us to calculate its size: it was a square, approximately 30 meters on a side, which would represent 100 feet of the classical Greek period. The pool was approximately 1.4 meters deep, meaning that it would have held well over 1000 cubic meters of water. Large drain facilities have been found (reused by the Romans) along the north side of the Roman bath-house. It is not known, precisely how the pool was filled, but presumably the water came from the large spring to the south-west that supplied the area with plentiful water until the 1950s CE.

Above the pool was a floor, partly set into it. The pool itself was certainly unroofed and set into it. The pool itself was certainly unroofed and open to the sky, but it is not known if the surrounding area was roofed. Presumably this Greek period bath was either part of or close to the gymnasium and other unexcavated. The classical bath, as much of has been uncovered now, is the largest that has been found from ancient Greece. Its pool is of a size much larger than the classical baths at Namea and Delphi, and similar to but still larger than that of Olympia. The Bath was certainly used by the athletes in the classical and the Roman periods, but whether it was also open to the ordinary visitors is unknown.

circa 450 BCE - 350 CE

Theater
The theater at Isthmia was situated on the slope of a shallow ravine, north-east of the plateau on which the temple of Poseidon was built. To create an adequate viewing area, one side of the ravine was excavated to form a three-sided cavea, which seated the audience. The orchestra was set at the base of this structure, significantly below ground level. A flume system, running along the line of the first row of seats, hints at the original seating arrangement. This first version of the theater was constructed in the second half of the fifth century BCE, aligning with the building of the classical period Temple of Poseidon and the stadium. Approximately a century later, the theater was renovated: the cavea was widened and given a curved shape, and a proscenium with 11 tourniquet-secured openings was added. This entire structure was wooden and could be dismantled between festival events.

During the Roman times, the games' return to the sanctuary spurred further expansion of the cavea, creating a 214-degree arc, and the stage was reconstructed, possibly in preparation for Emperor Nero's attendance at the 68/69 CE games. In the second century CE, plans were made to expand the cavea up to the top of the ravine, although only the foundations were completed. The stage building gained a Roman scaenae frons, with a high and narrow pulpitum. The two side entrances (parodoi) and the central stage passage were domed, and two 7.8-meter Ionic order columns, thought to have supported large statues, stood at the orchestra. Parts of these columns were later found in the walls of the Byzantine period fortress of "Examilia". Behind the stage, a large courtyard featured wooden colonnades along both sides, with roads on the east and west sides connecting the theater to yet unexcavated buildings to the north.

circa 440 BCE - 396 CE

Temple of Poseidon
In about 440 BCE, during the Classical period, the temple site was rebuilt as the Temple of Poseidon at Isthmia, directly over the remains of the original Archaic temple. The area remained highly active up until the third century CE, serving as a Panhellenic sanctuary and the last of the four Pan-Hellenic Games locations to be identified, with the games dating back to around 581 BCE. The site also included Roman baths, a theater, and two temples. The rebuilt Classical temple, however, suffered a similar fate to its predecessor, being destroyed by fire in 390 BCE. The Isthmian Games, held near the Temple of Isthmia in Poseidon's honor, were one of the four great athletic festivals of ancient Greece, alongside the games for Zeus at Olympia and Nemea and those for Apollo at Delphi. If the temple was still in use by the fourth century CE, it would have been closed during the late Roman Empire’s persecution of pagan sites. The Temple of Poseidon was likely sacked and destroyed during the Visigoth invasion of the Peloponnesus in 396 CE.

circa 323-30 BCE

Late Stadium
The Late Stadium, dating from the Hellenistic period, was constructed in a nearby streambed, with the stream diverted to flow beneath the track. Although the stadium remains largely unexcavated, it was partially explored in the 1950s. Covered by several feet of eroded soil and surrounded by a grove of trees at one end, the stadium has been challenging to excavate, but these limited findings offer insight into its layout and features. The racetrack lacks evidence of hard surfacing, unlike the Early Stadium, which used a white earth track surface. The Late Stadium’s water channels, lined with durable stucco, demonstrate a blend of Greek and Roman influences, with added basins for water storage. Some sections of the water system were adorned with paintings of marine animals, possibly honoring Poseidon. Seating steps cut into the banks on both sides of the track suggest spectator areas. Overall, the Late Stadium’s design reflects greater planning and sophistication compared to the Early Stadium, yet both demonstrate the cultural importance of athletic competition in ancient society.

circa 50 CE

Palaimonion
Originally an altar and a pine tree dedicated to the child-hero, Melikertes-Palaimon once stood near the shore. However, during the Roman period a circular shrine to Palaimon was situated at the southeast corner of Poseidon's temenos. Sacrifices of bulls were made to him and they were wholly consumed by fire in a series of three consecutive pits, the earliest of which belongs to the mid-first century CE. When excavated, the pits were filled with charred animal bones, lamps and vases left by the worshippers.

Palaimon's tomb was thought to be in a long tunnel (an abandoned reservoir) reached by a manhole to the west of the pits. Many lamps used in the night rites were discovered in front of it. A round temple was first built in the time of the Roman Emperor Hadrian (circa 117 to 138 CE) at the eastern side of Poseidon's shrine, where the remaisn of its square concrete foundation can be seen today. A few years later in the Antonine period (circa 138 to 196 CE) the temple was moved to the area of the pits and rebuilt to include a passage leading to the underground tomb. The foundation and passage are well-preserved. Images of the two temples appear on Roman coins of the period. A statue of Palaimon lying on a dolphin stood in its center.

It is notable that the Isthmian Games, according to legend, originally began as funeral games for the child-hero, Melikertes-Palaimon. When he and mother, Ino-Leukothea, leaped into the Saronic Gulf, a dolphin brought his body to the Isthmus where he was found and buried by Sisyphos, king of Corinth. His altar and pine tree stood on the shore. Also, as the dolphin-rider Palaimon, he, like his mother, was a patron of sailors and protector against shipwreck.

circa 150 CE

Roman Baths
The Roman Baths at Isthmia were constructed around 150 CE in an area of the Isthmian sanctuary and were most probably used by athletes. It was a building complex defined by luxury and beauty, with high roofs and enormous windows, lavishly decorated on both the exterior and interior. The walls of the baths were covered with decorated plaster or marble and the floors were covered with rich mosaics or slabs of colored marble. Four of the rooms were heated with great furnaces, and a complex in the northwest had two great cold pools. The baths would have been used not only for bathing but for social interaction and perhaps even for religious celebrations. Interestingly enough, the Roman period (circa 146 BCE - 324 CE) baths were constructed on the foundations of a bath structure dating back to the Classical period (circa 510-323 BCE), constructed around 360 BCE. This Bath, not fully excavated today, had a swimming pool 30 meters (100 Greek feet) on a side and 1.4 meters deep. The Roman Baths were used for 250 years until they were destroyed around 400 CE.

circa 1988 CE

Archaeological Museum of Isthmia
The Archaeological Museum of Isthmia, situated within the Sanctuary of Poseidon archaeological site, was designed by architect Pavlos Mylonas. The museum houses artifacts from a range of significant excavations in the surrounding region, including items from the Mycenaean cemeteries, the Sanctuary of Poseidon itself, the Roman baths, the defensive Justinian Wall, the hill of Rachi Isthmia, and the ancient port of Kenchreai. Among its most notable exhibits are glass panels from the temple of Isis, discovered at Kenchreai’s ancient port. These panels are among the few well-preserved examples of ancient glasswork, reflecting the port’s historical trade connections and religious significance in the region.